Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $169.94   7.283%   $182.3167   $182.32   $182.30   $182.30  
  Purchase #2 $212.48   6.681%   $226.6758   $226.68   $226.70   $226.70  
  Purchase #3 $183.47   6.696%   $195.7552   $195.76   $195.75   $195.80  
  Purchase #4 $66.70   13.267%   $75.5491   $75.55   $75.55   $75.50  
  Purchase #5 $23.48   5.544%   $24.7817   $24.78   $24.80   $24.80  
  Purchase #6 $25.35   12.560%   $28.534   $28.53   $28.55   $28.50  
  Purchase #7 $226.71   7.717%   $244.2052   $244.21   $244.20   $244.20  
  7 purchase totals = $908.13       $977.8177   $977.83   $977.85   $977.80